Many different unsaturated resins can be used in radical-curing molding materials, and examples include unsaturated polyester resins, epoxy (meth)acrylate resins (also referred to as vinyl ester resins), urethane (meth)acrylate resins, allyl ester resins, and (meth)acrylate ester oligomers. Depending on the intended application, a variety of different properties may be required of these unsaturated resins. In the case of molding materials used in bathtubs, boats or ships, vehicles, engineering and construction, and electronic components and the like, exposure to particularly severe environments can be expected, meaning a high level of performance is required. In order to achieve a molded product with excellent physical properties, water resistance, and corrosion resistance, epoxy (meth)acrylate resins can be used favorably for the applications described above.
Because an epoxy (meth)acrylate resin generally contains a large number of intramolecular hydroxyl groups generated by the reaction between an epoxy resin and (meth)acrylic acid, a molded product produced by curing such a resin typically exhibits a high coefficient of water absorption, and as a result, the water resistance and heat resistance tend to deteriorate with use. A molding material in which a polyisocyanate compound and a hydroxy compound are added, in specific proportions, to an epoxy (meth)acrylate resin is known to improve on this problem (see Japanese Patent (Granted) Publication No. 2,908,477).
Known methods of improving the hydrophilicity of the epoxy (meth)acrylate resins described above include the use of a photocurable resin composition for a coating material, which contains a liquid reaction product mixture obtained by reacting an epoxy resin, a (meth)acrylic acid anhydride, and (meth)acrylic acid, and also contains a photopolymerizable monomer and a photopolymerization initiator (see Japanese Examined Patent Application, Second Publication No. Sho 55-12043).
In addition, an example of a known vinyl ester resin (epoxy acrylate resin) that uses a similar technique is a liquid epoxy (meth)acrylate resin with a double bond equivalent weight of 170 to 200 for use as a coating material or an adhesive, produced by reacting an epoxy resin with a (meth)acrylic anhydride (quantity used: 0.9 to 1.0 mols per 1.0 mols of epoxy groups) (see U.S. Pat. No. 6,515,166).
Furthermore, curable resin compositions containing a resin such as a vinyl ester resin or unsaturated polyester resin, together with a carbon-based filler and a polyisocyanate have already been proposed as separators for fuel cells (see U.S. Pat. No. 6,251,308).
An unsaturated resin such as an epoxy (meth)acrylate resin or vinyl ester resin, obtained by reacting a (meth)acrylic anhydride with an epoxy resin, which is able to satisfy, to a high level, all of the aforementioned performance requirements such as handling properties, moldability that enables the filling of molding dies with complex shapes, and favorable molded product characteristics such as mechanical strength, corrosion resistance, and long term durability such as resistance to hot water, is as yet unknown. In addition, the use of an unsaturated resin for producing a fuel cell separator molded product that combines excellent conductivity and gas impermeability with excellent durability such as corrosion resistance, has also not yet been proposed.
An object of the present invention is to provide a curable resin composition for a molding material, which enables the production of a molded product such as the various electrical or electronic members which retains the favorable strength characteristics of an unsaturated resin in which (meth)acryloyl groups have been introduced into an epoxy resin (hereafter referred to as an epoxy (meth)acrylate resin), suffers no moldability problems such as the separation between the resin composition and any fillers during molding, or the occurrence of voids or warping, exhibits excellent filling characteristics for molding dies, exhibits excellent flowability and molded product external appearance during molding of the molded product, and also exhibits superior resistance to water absorption and superior hot water resistance, as well as to provide a fuel cell separator that uses such a curable resin composition, and exhibits excellent moldability, dimensional precision, conductivity, heat resistance, mechanical strength, and durability such as hot water resistance.